Effectiveness of mass dengue vaccination in the state of Parana, Brazil: integrating case-cohort and case-control designs

We aimed to estimate the effectiveness of CYD-TDV in preventing symptomatic dengue cases during a campaign targeting individuals aged 15-27 years in selected municipalities in Parana, Brazil. Additionally, we examined whether a history of dengue, as recorded by the surveillance system, modified the vaccines effectiveness. MethodsWe conducted a case-cohort analysis comparing the frequency of vaccination, with at least one dose of CYD-TDV, in individuals confirmed to have dengue by RT-PCR, identified by the surveillance system during 2019 and 2020, with the vaccination coverage in the target population. Moreover, with a case-control design using weighted controls, we assessed the history of dengue as a modifier of the vaccines effectiveness. The analyses were performed using a logistic random-effects regression model, with data clustered in municipalities and incorporating covariates such as the incidence of dengue before the campaign, age, and sex. ResultsDuring the study period, 1,869 cases of dengue were identified. The vaccination frequency among these cases was significantly lower than the overall vaccination coverage of the participating municipalities (50.4% vs. 57.2%, respectively; adjusted odds ratio: 0.79; 95% confidence interval: 0.72-0.87). In individuals with a history of dengue, vaccination was more than 70% effective in reducing the incidence of dengue. However, vaccination was not associated with significantly reducing the overall dengue case risk in individuals without a history of dengue. ConclusionVaccination significantly decreased dengue cases in the target population. The case-control design suggested that this reduction was primarily driven by the benefits seen in individuals with a history of dengue. Previous dengue diagnosis recorded by epidemiological surveillance could serve as a criterion for the recommendation of CYD-TDV, especially in endemic regions with limited serological testing facilities.